[Ennewi]

Originally Posted by Raev [You must be logged in to view images. Log in or Register.]

Just a reminder that your article compared masks to N95s, not masks vs none. It's hard to see this as relevant when virtually no one is wearing an N95 mask.

Likely because of hospital policy or because no patient would consent to their doctor forgoing the use of any mask. That one was shown to be more effective than the other implies that either would have been favorable over none at all. That isn't irrelevant.

Originally Posted by Raev [You must be logged in to view images. Log in or Register.]

Science clearly states that masks do not work. You can read the Danish study or a review by the British government here. TLDR: 8 randomized trials, 6 negative, 1 irrelevant (the one Ennewi found), and 1 that did find an effect in combination with hand sanitizer. The sad reality is that peer review and the scientific method are no match for billions of dollars in funding, and thus we have to read garbage like https://pubmed.ncbi.nlm.nih.gov/32329337/:

The conclusion is obviously completely unwarranted by the actual results.

If we can we agree not to use the word science as though we were quoting it directly, that would be a good start. At best, one might be referring to the scientific community or consensus among experts, which ought to be mentioned by name instead.

I am still reading through the Denmark link, but here's another link to serve as a counterargument which I am also still reading through...

https://www.pnas.org/content/118/4/e2014564118

There are no studies that have directly measured the filtration of smaller or lateral particles in this setting, although, using Schlieren imaging, it has been shown that all kinds of masks greatly limit the spread of the emission cloud (79), consistent with a fluid dynamic simulation that estimated this filtration level at 90% (80). Another study used a manikin and visible smoke to simulate coughing, and found that a stitched cloth mask was the most effective of the tested designs at source control, reducing the jet distance in all directions from 8 feet (with no mask) to 2.5 inches (81).

One possible benefit of masks for source control is that they can reduce surface transmission, by avoiding droplets settling on surfaces that may be touched by a susceptible person. However, contact through surfaces is not believed to be the main way SARS-CoV-2 spreads (82), and the risk of transmission through surfaces may be small (83).

In summary, there is laboratory-based evidence that household masks have filtration capacity in the relevant particle size range, as well as efficacy in blocking aerosols and droplets from the wearer (67). That is, these masks help people keep their emissions to themselves. A consideration is that face masks with valves do not capture respiratory particles as efficiently, bypassing the filtration mechanism, and therefore offer less source control (84).

Conclusion
Our review of the literature offers evidence in favor of widespread mask use as source control to reduce community transmission: Nonmedical masks use materials that obstruct particles of the necessary size; people are most infectious in the initial period postinfection, where it is common to have few or no symptoms (45, 46, 141); nonmedical masks have been effective in reducing transmission of respiratory viruses; and places and time periods where mask usage is required or widespread have shown substantially lower community transmission.

Footnotes
↵1To whom correspondence may be addressed. Email: jphoward@usfca.edu.
Author contributions: J.H., Z.L., H.-M.v.d.W., L.-H.T., V.T., R.S., and F.Q. designed research; J.H., A.H., Z.L., Z.T., H.-M.v.d.W., L.-H.T., V.T., R.S., and F.Q. performed research; J.H., A.H., Z.L., L.-H.T., V.T., F.Q., and C.M.R. analyzed data; and J.H., A.H., Z.L., Z.T., V.Z., H.-M.v.d.W., A.v.D., A.P., L.F., L.-H.T., V.T., G.L.W., C.E.B., R.S., F.Q., D.H., L.F.C., C.M.R., and A.W.R. wrote the paper.

The authors declare no competing interest.

https://en.wikipedia.org/wiki/Procee...tes_of_America

Proceedings of the National Academy of Sciences of the United States of America (often abbreviated PNAS or PNAS USA) is a peer-reviewed multidisciplinary scientific journal. It is the official journal of the National Academy of Sciences, published since 1915, and publishes original research, scientific reviews, commentaries, and letters. According to Journal Citation Reports, the journal has a 2019 impact factor of 9.412.[1] PNAS is the second most cited scientific journal, with more than 1.9 million cumulative citations from 2008 to 2018.[2] In the mass media, PNAS has been described variously as "prestigious",[3][4] "sedate",[5] "renowned",[6] and "high impact".[7]
PNAS is a delayed open access journal, with an embargo period of 6 months that can be bypassed for an author fee (hybrid open access). Since September 2017, open access articles are published under a Creative Commons license. Since January 2019, PNAS is online-only, although print issues are available on-demand.

Editors
The following people have been editors-in-chief of the journal:

1914–1918: Arthur A. Noyes
1918–1940: Raymond Pearl
1940–1949: Robert A. Millikan
1950–1955: Linus Pauling
1955–1960: Wendell M. Stanley
1960–1968: Saunders Mac Lane
1968–1972: John T. Edsall
1972–1980: Robert Louis Sinsheimer[23]
1980–1984: Daniel E. Koshland, Jr.
1985–1988: Maxine Singer
1988–1991: Igor B. Dawid
1991–1995: Lawrence Bogorad
1995–2006: Nicholas R. Cozzarelli
2006–2011: Randy Schekman
2011–2017: Inder Verma[24]
2018–2019: Natasha Raikhel
2019–present: May Berenbaum
The first managing editor of the journal was mathematician Edwin Bidwell Wilson.